One example of a rotary cutting tool assembly having a coupling arrangement of the above-specified kind is disclosed in EP 0742065. The assembly comprises first and second assembly components having interfitting male and female coupling members formed at their interacting faces, the coupling members having radially directed arm portions for torque transmission, and a centering portion located therebetween. The cutting tool is assembled by inserting the male coupling member within the female coupling member and coaxially coupling them together by a fastening screw.
The use of fastening screws in cutting tool assemblies of the above kind weakens the cutting tool and puts rather severe limitations on the miniaturization of the tool as far as cutting tools of small diameters are concerned, especially when these tools have axially extending chip flutes, and, consequently, do not have a cross-sectional area sufficiently large and a tool body sufficiently strong to accommodate appropriate fastening screws.
The problem is still more critical when rotary cutting tools are concerned, which have exchangeable cutting heads with a cutting edge extending to the center of the cutting tool, since it is inconceivable to secure such cutting heads by means of a central axial through-going fastening screw.
EP 0118 806 discloses a drilling tool assembly comprising a cylindrical tool shank formed with two chip flutes extending generally along a longitudinal axis thereof and a replaceable plate-like drilling head mounted thereto in a self-holding manner not requiring a fastening screw. The drilling head comprises two diametrically disposed substantially planar cutting portions in the form of cutting plates and the tool shank has a drilling head receiving slot defined between two diametrically disposed and radially oriented recesses formed at side surfaces of the chip flutes and extending therealong in the axial direction, the recesses mating with and being capable of receiving the cutting plates of the drilling head. The cutting plates and the recesses have narrow base surfaces oriented substantially perpendicular to the longitudinal axis of the tool and adapted to provide the axial support of the cutting head in the tool holder, and high side walls oriented transversely to the base surfaces and functioning as torque transmission walls.
It should be noted that, in the drilling tool as above, the relatively small width of the base surfaces is insufficient to withstand axial forces exerted on the tool during cutting operations. Furthermore, the drilling head with an elongated planar configuration as above is weak, when employed under torsion conditions. Furthermore, such tools have a small base area relative to the cross-sectional area of their tool shank and also relative to the height of their torque transmission walls, which leads to their instability. At least for these reasons, the drilling head of the above planar design is hardly applicable to small and, particularly, to miniature cutting tools.
It is the object of the present invention to provide a new cutting tool assembly and a new cutting head for use therein.